It has been fairly common practice for a number of years prior to the invention to manufacture dynamoelectric machine rotors by casting axially-extending conductors in rotor slots defined by aligned apertures punched in stacked laminations of such an assembly. It is also generally well known to provide axial coolant passageways and associated radial coolant ducts through such rotor assemblies in order to circulate cooling air along the central portion of the rotor assembly and then through the radial ducts, past the conductor bars. A variety of manufacturing methods have been developed to construct different types of laminated rotor assemblies utilizing cast conductor bars. A number of such prior art methods and resultant rotor assemblies are described in co-pending U.S. patent application Ser. No. 824,104 which was filed on Aug. 12, 1977 by the subject applicant and another employee of the assignee corporation, to which both that application and the present application are assigned. As is explained in that co-pending application, such prior art methods for constructing rotor assemblies frequently present common drawbacks and disadvantages, even though they have been employed successfully for a number of years. Perhaps the most universal and troublesome drawback of such prior art manufacturing methods is that they typically are relatively expensive and cumbersome to utilize because they require the employment of substantial amounts of manual labor to obtain the desired forms of cast conductors and rotor assemblies produced thereby. Due to the multiplicity of operating components, such as metal or ceramic casting pins that are necessarily employed in such prior art manufacturing processes to block casting metal from the ventilating ducts and passageways therethrough, occasionally one or more of such components will be slightly misplaced from its desired operating position, thus allowing molten metal to contaminate the coolant duct or passageway areas of the assembly. That contamination necessitates either additional manufacturing expenditures to remove such metal, or in some cases requires complete scrapping of the assembly. The invention disclosed in the above-identified co-pending patent application, in which a majority of the primary claims have now been held to be allowable by the U.S. Patent Office, comprises an improved laminated rotor assembly which is described in detail there. That assembly overcomes many of the shortcomings and disadvantages of earlier prior art rotor assemblies and associated methods of manufacture. The present invention, disclosed herein, is a further improvement over the type of laminated rotor assembly disclosed in that co-pending application, and the present invention includes a novel method for manufacturing such an improved rotor assembly.
Some advantages of the subject invention in addition to the economies of manufacture its use affords, are that the widths of radial cooling ducts can be increased relative to the sizes that might be usable with other methods of manufacture, such as the employment of casting pins to define cooling ducts in a rotor. Such larger ducts reduce the resistance to flow of cooling air, so will improve motor cooling relative to the performance of a rotor having its radial cooling duct widths limited more severely by the width of conductor slots in associated main rotor laminations. Also, with this invention, the conductor slots in the transition and duct laminations (described below) may be made with greater cross-sectional areas than the conductor slot areas in associated vent and main laminations (also described below). This possible variation allows greater design flexibility for the conductor slots in the main and vent laminae while maintaining a standardized conductor slot in the transition and duct laminae.